The present invention relates to a lens barrel for a photographic camera which includes a focussing device and also a mechanism for back adjusting.
As is well known, the lens barrel for a camera includes an outer barrel attached to the camera body, an inner barrel integrally composed with the lens system and arranged within the outer barrel and a focussing device. In previously known arrangements the inner barrel is coupled to the outer barrel by means of a helicoid screw or a pin slot coupling. The lens system is moved in conjunction with the inner barrel by adjusting the focussing device for focussing. Normally, in order to improve the accuracy of focussing with such a lens barrel, a back adjusting mechanism is provided in the lens barrel. Such a back adjustment is provided after the lens barrel has been completely assembled. After such assembly, the focussing device is adjusted so as to move the lens system to the position where the light from the infinite object focuses on an image plane of the film within the camera. The back adjusting mechanism is then adjusted so as to restrict the range of movement of the inner barrel with respect to the film plane, and to ensure that the inner barrel will be appropriately adjustable for focussing. Such an adjustment is usually referred to as back adjustment or adjustment for back focal length.
In the previously known systems where helicoid screws and pin slot couplings have been utilized for coupling the inner and outer barrels, and relatively large number of parts and corresponding increase in manufacturing costs have become a significant problem. Additionally, with such systems there is required a significant amount of time for the back adjustment to be made.